Each of the 4 major epicardial coronary arteries in 80 patients with fatal acute coronary events was divided into 5-mm long segments and a Movat-stained histologic section was prepared and examined from each segment. An average of 56 five-mm long segments were examined from each of the 80 patients. Of the 4016 five-mm segments of coronary artery examined, 1538 (38%) were 75 to 100% narrowed in cross-sectional area by atherosclerotic plaque (controls equal 3%), another 34% of the segments were 51 to 75% narrowed (controls equal 22%), 20% were 26 to 50% narrowed (controls equal 44%) and only 8% were 0-25% narrowed (controls equal 31). Thus, coronary atherosclerosis among patients with fatal acute coronary events is diffuse and severe.